When you are editing a Campaign in your T-Rex store admin (logged into yourdomain.com/wp-admin), you will see different columns and items you can modify.This screen shot shows you some of the positions of the columns and other campaign sections as they show up on your website.

Example of store admin Campaign screen. Notice the Columns and how they relate to the website view.

In this example, Left Column 1 contains "%product_description%" so it is pulling in the product description of the selected product. If you click a different small image, the description will change to that product's description.